Safety protection circuit

ABSTRACT

In the process of drilling a concrete in a buildings many times accidentally can be damage existing electrical conduit and the wires inside or plumbing pipes. All these damages can be avoided with a device which can indicate a grounded metal. Grounded metal is any metal object which is grounded to the existing electrical system in the building, such a conduit, plumbing pipes, supporting frames or metal beam.

BACKGROUND OF THE INVENTION

[0001] U.S. Pat. No. 4,089,031 of Stevens issued 1978 is known, relating to-“Safety Protection-Circuit”which comprises:

[0002] a power supply, three conductors (a hot wire, a neutral wire, a building ground wire), a step-down transformer, a primary winding (connected across the hot wire and the neutral wire), a secondary winding (connected across the input of a bridge rectifier), a fuse (interconnected between the hot wire and one side of the primary winding), the hot wire is also provided to one input of a ground fault interrupter circuit and a contact of a momentary push-button switch is provided, the neutral wire is tied to the second input terminal of the interrupter circuit and to one side coil of a relay which has five sets of contacts. The red indicator (red lamp) will become extinguished since the contact will be opened and the green indicator (green lamp) will light via the closure of the contact to indicate that the drill is ready for operation. Upon the event of the drill bit making contact with an electrically grounded conductive material, such as a metallic conduit carrying electrical cables therein which is beneath the concrete floor, the relay will become energized through the conductor which is connected to the housing ground of the drill. The switch on the drill is in its off-position. The red indicator (red lamp) will light again and the green indicator (green lamp) will now be extinguished.

[0003] Drawbacks of the known above mentioned device are the complexity of the electric circuit and its difficult embodiment for a manually operated drilling device for use in home environment. The safety effect protecting the drilling device from damage is achieved by often switching off the power of the device and more important using relays to activate the light indicators wich means that the light indicators are not self-contained ground indicators. As well this device is using transformer and rectifier which make it impossible to be install in to the drilling device.

SUMMARY OF THE INVENTION

[0004] The problem solved by the invention is to provide an instantaneous registration and visual signalization of the moment of contact of the drilling device to the grounded metallic object.

[0005] Object of the present invention is to provide the person operating the drilling device with the possibility to remove the drill from the drilling location without the necessity to switch off the power from the device.

[0006] Another object of the present invention is to provide a drilling device made of most technologically suitable, simplified and inexpensive materials and elements comprising an easily constructed electrical circuit.

[0007] Further object of the invention is the possibility of the incorporating of the electrical circuit into the case of the drilling device without any changes in its external appearance and dimensions.

[0008] The embodiment and enclosing into the case of the used drilling devices of the above mentioned visual light indication that is exceptionally important to the normal function of the drilling device, will be carried out extremely easily and technologically correctly.

[0009] Another object of the present invention is to provide an improved safety protection circuit which has indicating means for indicated the point of contact of tool to the ground metal. The indicating means consist: a power source, two conductors consist of a hot wire and ground wire, one neon bulb whit resistor, two indicators: the first indicator is a red light emitting diode /red LED/ and the second indicator is a green light emitting diode /green LED/ and two diodes.

[0010] Further object of the present invention is improvement safety protection circuit for use in conjunction with electrically-operated power tools such as drills.

[0011] Yet another object of the present invention is to provide a safety protection circuit in which the first indicator /red LED/ has lower voltage drop respectively lower resistance than the second indicator /green LED/.

[0012] Both light emitting diodes connected with common anodes to one end of the neon bulb. The second end of the neon bulb is connect to the hot wire from the power line through resistor The second indicator /green LED/ cathode connected to the ground wire from the power source.

[0013] The function of the neon bulb is to insulate the power line from the circuit and by means of resistor to supply low voltage to the /red LED/ and /green LED/.

[0014] The first indicator /red LED/ cathode connected to the metal corpus of the drill through a diode.

[0015] An indicating means is provided for visually displaying the operative condition of the tool This indicating is achieve with two LED which are integrated in way of which the second indicator /green LED/ drains from the first indicator /red LED/ the small current which appear when the bit of the drill is in the concrete which has some conductivity but still the current is not enough to power up the first indicator /red LED/. This /red LED/ is lighting only when the current is large enough, this occur when the bit from the drill hits the grounded metal and informing the operator that the drilling device is in contact with such object. Without the second indicator /green LED/, the first indicator /red LED/ starts to flash even when the bit is in the concrete.

DETALLED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] The safety protection circuit of the present invention is described for use in conjunction with a drill which is utilized for penetrating in an electrically non-conductive material such as a concrete and an electrically conductive material such as a grounded metal. Referring now in detail to the schematic diagram FIG. 1, the safety protection circuit is mounted in a housing. A power to the circuit is provided through two conductors—a hot wire 5 and building ground wire 6. The neon bulb 1 with resistor 11 is connected in series between the hot wire 5 and the common anodes on the red LED 2 and green LED 8.

[0017] The cathode of the green LED 8 is connect to the building ground wire 6 through diode 9. The functions of the neon bulb 1 and the resistor 11 are: to insulate the power line from the circuit and to supply low voltage to the red LED 2 and green LED 8. The functions of the diode 9 and diode 10 are to protect the first indicators LED 2 and the second indicator LED 8 from reverse voltage.

[0018] There are two indicators: the first indicator is a red light emitting diode LED 2 and the second indicator is a green light emitting diode-LED 8. The red LED 2 with voltage drop lower respectively lower resistance then the green LED 8 connected with common anodes to the one end of the neon bulb 1, the second indicator green LED 8 cathode connected to the building ground wire 6 through diode 9. The first indicator red LED 2 cathode connected to the metal corpus of the drill respectively to the drill bit through diode 10.

[0019] The functions of the second indicator- green LED 8 are: first to show when is lighting that the safety protection circuit is powered up respectively the power toll.

[0020] Second function to show when is lighting that the safety protection circuit is powered up correctly because if for some reason the hot and neutral wire from the power source are switched over the safety protection circuit will not operate.

[0021] Third function when is lighting to drain from the first indicator red LED 2 the small current which appears when the bit of the drill is in the concrete which can provoke the red LED to flash. In this case the current flow through the path with less resistance which is the path throughout the second green indicator instead the path of the first red indicator wich is going through the higher resistance of the concrete.

[0022] Without the second green indicator the first red indicator starts to flash even when the drill bit is in the concrete because there is no element which can drain this small current conduct through the concrete.

[0023] The function of the first indicator red LED 2 is: when flashing to indicate the moment of contact on the drill bit with the grounded metal object. In this case the current is going through the path of the first red indicator, which path has less resistance than the path through the second green indicator whish cost the first red indicator to flash.

[0024] There is a second way of detecting ground metal as showing on FIG. 2, using only one of the wires from the power tool; in this case the hot wire can only be used for the safety protection circuit. The second method is different from the first method because a building ground wire is not needed to operate the safety protection circuit.

[0025] The second type of safety protection circuit comprises a single indicator red LED 2 connect with the anode to the low voltage power supply through first diode 12 and second resistor 14. Said lower voltage power supply comprises neon bulb 1 and first resistor 1. The cathode of said indicator red LED 2 connected to the corpus of the drill through the second diode 10. The function of the first diode 12 is to rectify AC to DC voltage. The function of the second diode 10 is to protect from reverse voltage in case the bit hit a hot wire.

[0026] The safety protection circuit also comprising a capacitor 13 connected with its positive end in between the cathode of the first diode 12 and the second resistor 14.

[0027] The negative end of said capacitor connected to the cathode of said indicator red LED 2. The function of the capacitor 13 is to charge quickly and to discharge slowly to steady voltage across the indicator red LED 2.

[0028] The second resistor 14 connect with one end in between the cathode of diode 12 and positive end of the capacitor 13, and other end connect in between the anode of the indicator red LED 2 and the third resistor 15. The function of the second resistor 14 is to allow the capacitor 13 to be charge fast and discharge slow.

[0029] The function of the capacitor 13 is to keep the charge and to supply steady voltage across indicator red LED 2.

[0030] Third resistor 15 connect in between the anode and cathode on the indicator red LED 2.

[0031] The function of the third resistor 15 is to prevent the indicator red LED 2 to light up at low current which appears when the bit of the drill is in the concrete. Without resistor 15, indicator red LED 2 will light up when the drill bit is in the concrete ,because the concrete has some conductivity.

[0032] Optional can be use a second pair of low voltage power supply comprising a resistor 16 and neon bulb 17 which are connected in series to the neutral wire and the anode of the diode 12. The function of this second low voltage power supply is to power up the safety protection circuit in case of miss wiring between the hot and the neutral wire. 

What is claimed is:
 1. A safety protection circuit for indicating ground metal contact for use with an electrically-operated power tool comprising: Low voltage power supply connect between the hot wire and the common anodes on the first and second indicator. Said first indicator connect with the cathode to the drill corpus through first diode, and said second indicator connect with the cathode to the building ground wire through the second diode; First indicator means for indicating to the user that the electrically-operated power tool has contacted ground metal; Second indicator means for indicating to the user that the electrically-operated power tool is powered properly; Circuit means which is connectable to the power source of the electrically-operated power tool and the first indicator means and the second indicator means, permitting the second indicator means to indicate to the user that the electrically-operated power tool is operational during normal use and causing the second indicator means to withdraw indication of operation and the first indicator means to indicate contact with ground metal upon contact having occurred during use. Said first indicator means having a voltage drop of a first magnitude and said second indicator means having a voltage drop of a second magnitude, said first magnitude equal or lower than said second magnitude, and there is provided a connection means which operatively connects both the first indicator means and the second indicator means to the power source and the corpus of the electrically power tool. Said low voltage power supply means; there being an insulating means for insulating the high voltage power source of the electrically operated power tool from the circuit and reducing the voltage to a range that is acceptable for the operation of the device.
 2. A safety protection circuit for indicating ground metal contact for use with an electrically-operated power tool comprising: First and second indicators connect with one of there end to the power source from said electrically-operated power tool. Second end from said first and second indicator connected to the corpus on said electrically-operated power tool. Said first indicator means and the second indicator means, causing the second indicator means to withdro indication of operation and the first indicator means to indicate contact with ground metal upon contact having occurred during use. Said first indicator means having a voltage drop of a first magnitude and said second indicator means having a voltage drop of a second magnitude, said first magnitude lower than said second magnitude.
 3. A safety protection circuit as claimed in claim 1 wherein the insulating means comprises a neon bulb.
 4. A safety protection circuit as claimed in claim 1 wherein said reducing the voltage means comprises a resistor.
 5. A safety protection circuit as claimed in claim 1 wherein said first indicator means comprises a red light emitting diode.
 6. A safety protection circuit as claimed in claim 1 wherein said second indicator means comprises a green light emitting diode.
 7. A safety protection circuit comprises a single indicator red light emitting diode connect with the anode to the low voltage power supply through first diode and second resistor. Said lower voltage power supply comprises neon bulb and first resistor. The cathode of said indicator red light emitting diode connected to the corpus of the drill through the second diode. The safety protection circuit also comprising a capacitor connected with its positive end in between the cathode of said first diode and to the said second resistor. The negative end of said capacitor connected to the cathode of said indicator red light emitting diode. Said second resistor connect with one end in between the cathode of said first diode and to the positive end of said capacitor, and other end connect in between the anode of said indicator red light emitting diode and to the third resistor. Said third resistor connect in between the anode and cathode on said indicator red light emitting diode. A second low voltage power supply connect in series between the neutral wire and the anode of said first diode.
 8. A safety protection circuit as claimed in claim 7 wherein said second low voltage power supply means comprises a resistor and neon bulb. 